Frequently Asked Question

How do I identify a flexible joint that causes chatter?
Last Updated 3 months ago

To determine the source of vibrations, please see the FAQ “Troubleshooting the source of vibrations during machining”.

If the tool side is causing chatter:
(You can use 1D modal analysis and look at Lathe example in CUTPRO’s Example folder: C:\Program Files (x86)\CutPro\Examples\Modal Analysis\1D Modal Analysis)

1) Mark points along the tool – fixture – spindle (i.e. tool tip-1, middle of the stick out-2, close to the tool holder-3, tool holder but close to the tool clamping-4, tool holder close to the spindle flange–5, spindle nose-6). Stick the accelerometer at the tooltip (Point 1) and keep it at point 1, and apply impact at point 1 (FRF Measurement H11), point 2, …, point 6.
2) Load the measurements into CutPro Modal Analysis Module; select the high peaks (natural frequencies), especially the one which is close to the chatter frequency.
3) Display the mode shape which corresponds to the chatter frequency. Mode shape will show you how the tool-holder-assembly is behaving during chatter.

• If the mode shape shows that the deflection is a continuous from the spindle nose-holder-tool, the whole spindle is vibrating.
• If the tool holder is sharply deflecting away from the spindle nose, the holder-spindle interface is either worn or connection is weak due to dust or chip stuck in the spindle taper. If not, the holder is weak.
• If the tool is deflecting away from the holder-joint sharply, the tool-holder joint is not stiff enough. Tighten the holder or use shrink fit. If the tool is deflecting with the curved shape, the tool is too long and flexible.

If the workpiece side is chattering
(You can use 2D modal analysis example in the CUTPRO Example folder C:\Program Files (x86)\CutPro\Examples\Modal Analysis\2D Modal Analysis)

1) Mark points on the XY plane of the workpiece – fixture set up. Stick the accelerometer at one point (1) which seems to be most flexible.
2) Apply impact at each point while keeping the accelerometer at the same point (Point 1), and save the measurements.
3) Load the measurements in Modal Analysis (2D analysis). Check the mode shape which has the closest natural frequency with the chatter frequency. Mode shape will show you the clamping or workpiece locations which deflect most. If the deflections occur at the workpiece – fixture contact points, place the clamps at the points where you see the largest mode shape deflections.

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